1. Field of the Invention
The present invention is related to a radiation imaging cassette. More specifically, the present invention is related to a radiation imaging cassette which is capable of communicating with an external console that issues imaging commands.
2. Description of the Related Art
Presently, various radiation imaging apparatuses, for obtaining radiation images to be utilized for medical diagnoses and the like, have been proposed and are in practical use. These radiation imaging apparatuses employ solid state detectors (having semiconductors as main components thereof) as radiation image detecting means. The solid state detectors detect radiation that has passed through subjects, and obtain image signals that represent radiation images of the subject.
A variety of formats have been proposed for the solid state detectors to be utilized in these apparatuses. Regarding a charge generating process for converting radiation to electrical charges, there are solid state detectors of a photo conversion type, and solid state detectors of a direct conversion type, for example. A solid state detector of the photo conversion type temporarily stores signal charges, obtained at a photoconductive layer by detecting fluorescence emitted by phosphors due to irradiation with radiation, in a charge accumulating section, then converts the accumulated charges to image signals (electrical signals) and outputs the image signals. The direct conversion type of solid state detector temporarily stores signal charges, generated within a photoconductive layer due to irradiation with radiation and collected by a charge collecting electrode, in a charge accumulating section, then converts the accumulated charges to electric signals and outputs the electric signals. In this type of solid state detector, the main components are the photoconductive layer and the charge collecting electrode.
Regarding a charge readout process for reading out the accumulated charges, there are an optical readout method and a TFT readout method. In the optical readout method, accumulated charges are read out by irradiating a solid state detector with readout light (electromagnetic waves for readout). In the TFT readout method, accumulated charges are read out by scanning TFT's (thin film transistors), which are connected to a charge accumulating section. The TFT readout method is disclosed in U.S. Pat. No. 6,828,539.
An improved direct conversion type solid state detector has also been proposed in U.S. Pat. No. 6,268,614. The improved direct conversion type solid state detector is a solid state detector of the direct conversion type that utilizes the optical readout method. This solid state detector comprises: a recording photoconductive layer that exhibits photoconductivity when irradiated by recording light (radiation, or fluorescence generated by the irradiation of radiation); a charge transport layer that acts substantially as an insulator with respect to charges having the same polarity as latent image charges, and that acts substantially as a conductor with respect to charges having the opposite polarity as latent image charges; and a readout photoconductive layer that exhibits photoconductivity when irradiated by electromagnetic waves for readout; stacked in this order. Signal charges (latent image charges) that bear image information are accumulated at an interface (charge accumulating section) between the recording photoconductive layer and the charge transport layer. Electrodes (a first conductive layer and a second conductive layer) are provided on both sides of the three aforementioned layers. In the solid state detector having this format, the recording photoconductive layer, the charge transport layer, and the readout photoconductive layer are the main components.
Recently, various radiation imaging cassettes, in which the aforementioned solid state detectors are contained in small housings, have been proposed. These radiation imaging cassettes are comparatively thin and of portable sizes. Therefore, a radiation imaging cassette can be placed under a portion of a patient to be imaged, and a radiation source can be placed at a position that faces the radiation imaging cassette with the patient sandwiched therebetween, to perform imaging even if the patient is immobile. The radiation imaging cassettes enable imaging with a high degree of freedom.
There are radiation imaging cassettes which are connected to external consoles during imaging. Imaging information, such as patient ID information, is obtained by the radiation imaging cassettes from the external consoles, and obtained image data are transmitted from the radiation imaging cassettes to the external consoles after imaging operations. There are radiation imaging cassettes of this type that perform communications with the external consoles wirelessly, as disclosed in U.S. Patent Application Publication No. 20060280337.
In a radiation imaging cassette which is capable of communicating wirelessly with an external console, radio waves are constantly being transmitted while the cassette is powered ON, to establish communication with the external console. Therefore, there is concern that if the cassette approaches a patient who has a pacemaker implanted in his or her body, adverse influence may be exerted onto the pacemaker by the radio waves.
Japanese Unexamined Patent Publication No. 2005-176973 discloses a radiation imaging method that takes the influence exerted onto pacemakers by wireless communications into consideration. In this radiation imaging method, obtained images are analyzed, and wireless output is increased when it is confirmed that a pacemaker is not implanted in a patient. However, in this method, whether a pacemaker is implanted cannot be judged unless patients are imaged once. Therefore, the possibility of unexpected accidents occurring cannot be denied.
In view of the foregoing points, there is demand for a radiation imaging cassette which is capable of performing imaging operations safely, even in cases that patients with pacemakers are in the vicinity of the radiation imaging cassette.